1. Field of the Invention
This invention relates to a coprecipitation method for producing high transition temperature (Tc) powdered superconducting oxides, such as YBa2Cu307-x, and more particularly to a coprecipatation method by which superconducting powders of Y-Ba-Cu-O with a high degree of homogeneity can be mass produced.
2. Description of the Prior Art
Hitherto, in general, three major methods of producing powdered oxide superconductors which have higher transition temperatures have been developed, namely, the solid-state reaction method, alcoholate processing method, and coprecipitation method. By using the solid-state reaction method, a series of laborious cycles of heating and grinding to metal oxides or carbonates as starting materials, have to be processed, and the compositional inhomogeneity of the final obtained powders can not be avoided. In the alcoholate processing method, starting materials, such as Yttrium (Y), Barium (Ba), and Copper (Cu) alcoholates, have been treated by a serious of processes, i.e. mixing, hydorlysis, drying, grinding, roasting, and sintering, etc., so as to obtain the superconducting powders. However, due to the difficulties of the preparation of the starting materials and the expensive cost of the starting materials, it is not suitable for mass production. In order to reduce the production cost and to obtain better controlled stoichometry so as to inturn obtain a higher homogeneity, the coprecipitation method has been employed by various workers. The most known coprecipitation method uses oxalate ions as precipitants in the aqueous Yttrium (Y), Barium (Ba), and Copper (Cu) nitrates solution, and uses potassium hydroxide (KOH) to adjust the PH value of the solution thereby causing coprecipitation of Y, Ba, and Cu. However, there are still some disadvantages in the known coprecipitation method, such as the fact that the homogeneity of the precipitated powders is not as satisfied as expected due to a locally uneven distribution of PH value was made by the KOH in instaneousness. A part of superconductivity might be lost in the precipitated powders since a possible contamination of potassium ions, and undesirable stoichiometry can not be avoided.